In present vehicle engine design, the carburetor or fuel injection system is provided with an idle air computer system controlled by the vehicle engine control module (ECM). This comprises a fuel injection system of the throttle body injection type with an idle air inlet at the venturi adjacent the throttle valve. The volume of idle air inlet is controlled by an idle air valve which is actuated by a coil-type solenoid. The engine idle speed is controlled by the ECM in response to various engine parameters by controlling the energization of the solenoid. A pulse width modulator in the ECM produces pulses of variable width for energizing the solenoid for displacement control of the valve. Without pulse modulation, full power supplied to the solenoid would result in full opening of the valve and no power supplied to the solenoid would result in full closing of the valve. By pulse width modulation, the degree of opening may be controlled. A bias spring is attached to the valve to bias same to the closed position.
One tester for an idle air intake valve is disclosed in U.S. Pat. No. 4,764,727 issued Aug. 16, 1988 in the name of McConchie, Sr. A monitor circuit is inserted between the engine control module (ECM) and the idle air control motor of the air intake valve. The idle air control motor includes two separate coils to enable the valve to have stepping characteristics in two directions. A first pair of LEDs are connected to the first coil and a second pair of LEDs are connected to the second coil. The LEDs illuminate intermittently during normal operation and are held in one condition during abnormal operation.
A general object of this invention is to provide an improved idle air control system tester with a pulse width modulation monitor and a selective manual control circuit to overcome certain disadvantages of the prior art.